JPS6157981B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refrigerant flow rate control device for a refrigeration cycle using a variable capacity compressor.

FIG. 1 is a schematic diagram of a refrigeration cycle using a variable capacity compressor. 1 is a variable capacity compressor, 2 is a condenser, 3 is an electric expansion valve whose throttle amount can be adjusted by an electric signal, and 4 is an evaporator. 5 is the temperature detected by a first temperature sensor 50 provided in the middle part of the evaporator 4 (this may also be the inlet part)
The difference between T ₁ and the temperature T ₂ detected by the second temperature sensor 51 provided at the outlet of the evaporator 4 SH' = T ₂ -
The state of the refrigeration cycle is detected by T ₁ , and the electric expansion valve 3 is activated so that this temperature difference SH' becomes a predetermined value SH' _R.
This is an aperture control device that outputs an electric signal to control the aperture amount of the aperture. Reference numeral 6 denotes a capacity control device that controls the capacity of the variable capacity compressor 1 according to the output of a state detector 61 that detects the state of the object to be frozen in the refrigeration cycle. If a refrigeration cycle is used in an air conditioner, the condition detector 61 is, for example, a room temperature detector.

FIG. 2 is a diagram for explaining the relationship between the temperature difference SH' and the throttle amount O _v of the electric expansion valve 3. Assume that the capacity of the variable capacity compressor 1 is switched between two stages, high and low, and O _v -SH' during low capacity operation is shown as a solid line (cycle 1), and that during high capacity operation is shown as a broken line (cycle 2). show. It is assumed that during operation in cycle 1, a predetermined temperature difference SH'R is obtained with the throttle amount O _v1 . When switching from this state to cycle 2 of high capacity operation, the temperature difference SH' obtained becomes SH' _B if the throttling amount remains O _v1 . While the change from cycle 1 to cycle 2 is abrupt,
The response speed of the second temperature sensors 50, 51 is slow;
Furthermore, if the electric expansion valve 3 has a valve drive unit that combines an electric heater and a bimetal, the response of the throttle amount will be slow. Therefore, the operating point when changing from cycle 1 to cycle 2 is A in Figure 2.
Move from to B. At this time, the control device 5
Since SH' is SH' _B which is smaller than the predetermined value SH' _R , the aperture amount is further reduced and an electric signal is outputted to increase the temperature difference SH'. However, it is clear from FIG. 2 that even if the throttle amount is further reduced from point B in cycle 2, it is not possible to move to the predetermined operating point C.

In the above explanation, in order to simplify the explanation, the variable displacement compressor 1 was explained using as an example a variable capacity compressor 1 that switches between two stages of high and low levels, but even in the case of a variable capacity compressor 1 that switches in multiple stages or one that switches continuously, it is possible to switch from cycle 1 to cycle 2. The above-mentioned problems also occur due to the delay in the response of the refrigerant flow rate control device comprising the control device 5 and the electric expansion valve 3 to changes in the temperature.

It is an object of the present invention to eliminate the drawbacks described in the above-mentioned conventional example and to obtain a refrigerant flow rate control device that does not fall into an uncontrollable region with respect to changes in the capacity of a variable capacity compressor.

FIG. 3 is an electrical circuit diagram of a control device according to an embodiment of the present invention. 50', 51' are thermistors as the first and second temperature sensors 50 _{, 51, and an operational amplifier 53 (SH' R −} SH') is amplified to obtain a voltage V _T , which is amplified by an operational amplifier 56 and a transistor ₅₇ via a relay 5R that selects a voltage V The voltage is applied to the energized closed type electric expansion valve 3' as the energized closed type electric expansion valve 3 to control the amount of restriction thereof. i.e. resistance 5
4, 55, a capacitor 58, an operational amplifier 59, a relay 5R, etc. constitute the aperture amount changing section 7. 1' is an example of the variable capacity compressor 1, which is a compressor that switches its capacity into two levels, high and low, where L is a low capacity and H is a high capacity. The capacity control device 6 outputs the relay 61, and by turning on the relay 61, high capacity,
Control to low capacity by turning off. relay 5
R is turned on because the output of the operational amplifier 59 is L _O during the time t from when the relay 61 is turned on until the charging voltage V _C of the capacitor 58 reaches _VR , and is turned off otherwise. The voltage applied to the electric expansion valve 3' is V _i during the time t when the relay 5R is on, and V _T is applied at other times.

Now, relay 61 is off, compressor 1' is operating at low capacity, voltage V _T is applied to electric expansion valve 3', and temperature difference SH' is controlled to SH' _R. shall be. When the load increases from this state and high capacity operation becomes necessary, the relay 61 is turned on and the compressor 1' operates at high capacity. At the same time, relay 5R is turned on, and voltage V _i is applied to electric expansion valve 3'. This voltage V _i is selected so that the amount of throttling of the electric expansion valve 3' is equal to or greater than the amount of throttling O _v2 shown in FIG. 2. In Figure 2, when changing from cycle 1 to cycle 2, the throttling amount is forcibly shifted from O _v1 to O _v2 or more by relay 5R, and after that, the refrigeration cycle is almost stable. reached, thermistor 50', 51', electric expansion valve 3'
follows the change in the cycle, that is, the time t
After the elapse of , the relay 5R is turned off and the voltage applied to the electric expansion valve 3' becomes equal to the output voltage V _T of the operational amplifier 53.

According to the above-mentioned control device, when changing from cycle 1 to cycle 2, in anticipation of a delay in the refrigerant flow rate control system, the throttle amount of the electric expansion valve is controlled by a constant voltage V _i that does not depend on the temperature difference SH' for a time t. Since the throttle amount is set to (>O _v2 ), stable control can be performed without falling into an uncontrollable state.

In the above example, the compressor 1 has been described in which the capacity is changed in two stages, high and low, but the same applies to the case where the capacity is changed in more stages.

FIG. 4 shows an embodiment of a control device when a compressor whose capacity can be continuously varied is used as the variable capacity compressor 1. 12 is a continuously variable compressor, and the capacity control device 6 includes a capacity determining circuit 6A that determines the capacity from the output of the state detector 61, and a rotation speed that controls the rotation speed of the compressor driving electric motor according to the output of the capacity determining circuit 6A. It consists of a control circuit 6B. Rotation speed control circuit 6B
is, for example, an inverter when the compressor driving electric motor is an induction motor. 501 indicates the difference between the signals from the thermistors 50' and 51', that is, the difference between the temperature difference SH' and the predetermined value SH' _R , and the inverter 50 described later.
502 is an amplifier that amplifies the output of the amplifier 501, and applies the output of the amplifier 502 to the electric expansion valve (energized closed type) 3'.
503 is a differentiator that differentiates the output of the capacitance determining circuit 6A, and 504 is an inverter that inverts the output of the differentiator 503. The differentiator 503 and the inverter 504 constitute the aperture amount changing section 8.

When the compressor 12 is operated at a constant capacity, the output of the capacity determining circuit 6A is constant, and the output of the differentiator 503 is constant.
The output is zero volts and the inverter 504 output is also zero volts. Therefore, the voltage applied to the electric expansion valve 3' becomes the voltage V _A obtained by amplifying the difference between the temperature difference SH' and the predetermined value SH' _R by the amplifier 501. If the capacitance is increased, the output of the capacitance determining circuit 6A increases, the output of the differentiator 503 becomes -V _D and negative, and the output of the inverter 504 becomes +V _D
becomes positive. The amplifier 501 has a voltage of +V _D ,
Since the voltage corresponding to the difference between the temperature difference SH' and the predetermined value SH' _R is added and amplified, its output decreases, and as a result, the voltage applied to the electric expansion valve 3' decreases, so its throttling amount becomes (Since the electric expansion valve 3' is an energized closed type, the larger the applied voltage, the smaller the throttle amount.) Therefore, for example, when changing from cycle 1 to cycle 2 in FIG. 2, the throttle amount of the electric expansion valve 3' can be increased,
It is possible to avoid the uncontrollable region that occurs when the throttle amount is controlled based on the temperature difference SH'.

As detailed above, according to the present invention, the problem that occurs in conventional control systems, such as entry into an uncontrollable region due to a delay in the response of the refrigerant flow control system to changes in the refrigeration cycle, is solved, and stable operation is always performed. The refrigerant flow rate control device provides excellent effects.

[Brief explanation of the drawing]

Figure 1 is a refrigeration cycle configuration diagram using a variable capacity compressor, and Figure 2 is the temperature difference with respect to the throttling amount O _v .
FIG. 3 is an electric circuit diagram of a refrigerant flow rate control device according to one embodiment of the present invention, and FIG. 4 is an electric circuit diagram of a control device according to another embodiment of the present invention. 1... Variable displacement compressor, 3... Electric expansion valve,
6... Capacity control device, 7, 8... Throttle amount changing unit,
50, 51...first and second temperature sensors as refrigeration cycle state detectors, 61...state detector.

Claims (1)

[Claims] 1. A refrigeration cycle having a variable capacity compressor and an electric expansion valve, a refrigeration cycle state detector for detecting the state of this refrigeration cycle, and controlling the throttle amount of the electric expansion valve according to the output of the state detector. a throttling amount control device, a state detector that detects the state of the object to be frozen, and a capacity control device that controls the capacity of the compressor according to the output of the state detector,
When the output from the capacity control device is an increase in capacity, the throttling amount control device detects this and adjusts the throttling amount of the electric expansion valve for a predetermined time to a larger opening than the previous throttling amount. A refrigerant flow rate control device configured to include a throttle amount changing section that changes the amount.